If you use a language other than English (what, there are Mac users outside of America? ;-), you might want to give ObjectFarmSpell a look. ObjectFarmSpell adds the ability to spellcheck the German, French, Spanish and Italian languages from within most any Cocoa app.

How does it do this? In an example of the benefits of putting a full UNIX core under a consumer OS, ObjectFarmSpell is simply a set of hooks that connects Cocoa apps with ispell, an international spell checker for UNIX that's been around since 1971.

If you want to spell check non-English languages within Cocoa apps, try ObjectFarmSpell. Note that this is still a beta release, and there are more languages and features planned in the future.

It works but not as service but you have to select the spell option in (I tried TextEdit and Mail) and select another dictionary as active one. This is how it is intended to work, the service extension is just a bit misleading